The present invention relates to the preparation of linear and cyclic fluorinated C.sub.4 to C.sub.6 hydrocarbons by catalytic hydrogenation of appropriate haloolefins, to novel cyclic fluorinated hydrocarbons, and to the use of fluorinated C.sub.4 to C.sub.6 hydrocarbons as propellant gas and working fluid for heat pump systems.
Processes for preparing special fluorinated C.sub.4 hydrocarbons are known. Thus, 1,1,1,4,4,4-hexafluorobutane can be prepared by reacting succinic acid with sulfur tetrafluoride. W. Dmowski et al, PL Inventor's Certificate 87,481. This process is unsatisfactory since it requires sulfur tetrafluoride, which is not only toxic but is accessible only by an uneconomical method. 1,1,1,4,4,4-Hexafluorobutane can also be prepared by hydrogenating 1,1,1,4,4,4-hexafluoro-2-chloro-2-butene or 1,1,1,4,4,4-hexafluoro-2,3-dichloro-2-butene catalytically in the presence of palladium on aluminum oxide (Y. Huang et al, Youji Huaxve, 2, 125 (1984)), but the product of this process is always obtained in the form of mixtures with chlorine-containing compounds. However, according to more recent reports (see J. F. D. Mills, Cell. Polym., 5, 343 (1987) and F. S. Rowland et al, Nature, 249, 8 (1974)), the chlorine contained in conventional propellant gases causes damage to the ozone layer of the earth's atmosphere. Finally, 1,1,1,4,4,4-hexafluorobutane can also be prepared by hydrogenation of 1,1,1,4,4,4-hexafluoro-2-butene. R. N. Haszeldine, J. Chem. Soc., 2504 (1952). The disadvantage of this process is that a difficulty obtained and expensive starting material must be used. R.N. Haszeldine, J. Chem. Soc., 2504 (1952).
1,1,2,2-Tetrafluorocyclobutane can be prepared by reaction of tetrafluoroethylene with ethylene in a "two +two" addition. D. Coffman et al, J. Amer. Chem. Soc., 71, 490 (1949). However, the yield of this reaction is not satisfactory.